Ultraviolet radiation A (UVA) penetrates deeper in human skin than ultraviolet radiation B (UVB) and has been shown to account for the deeper mutations found in squamous cell carcinoma skin cancers. UVA is known to be a potent inducer of singlet oxygen, a known mutagen. Physical Sciences Inc. (PSI) and the Sivamani research group at the University of California at Davis (UCD) propose to develop an instrument with the sensitivity required to detect the weak luminescence caused by singlet oxygen generated under typical solar illumination. PSI has developed a prototype instrument platform that has previously been used to demonstrate real-time, in vivo measurements of singlet oxygen generation from skin in healthy human subjects and from tumor-laden rats undergoing photodynamic therapy. During the proposed SBIR development program, PSI will improve the instrument sensitivity by adding a novel tunable spectral filter and optical detection system to provide the increased sensitivity required to measure the weak singlet oxygen luminescence signal emitted through the skin. PSI will fabricate and calibrate the instrument to demonstrate a singlet oxygen concentration detection limit of 5 picomolar. PSI scientists will then transport the novel sensor t UCD to demonstrate its use in measuring singlet oxygen production in ex vivo and in vivo measurements of human skin of different types. PSI will work with leading vendors of skin therapies including Bayer Healthcare to create an instrument optimized for widespread use in product development and research. The resulting commercial product will find application in the cosmetic and pharmaceutical industries to develop and characterize novel skin therapies for different skin types to reduce the incidence of skin cancer and UV-induced skin lesions.